Conventionally, in a high-speed digital transmission, pre-emphasis is used to condition an output of a transmitter. In transmitting data, such transmitted data may be distorted due to any of a variety of factors, including without limitation, a transmission medium such as a transmission line or lines for example. Such distortion may be more pronounced when transmitting data at high transfer rates. For example, Peripheral Component Interconnect Express (“PCIe”) 3.0 is at approximately 8 gigatransfers per second (GT/s). Pre-emphasis may be used to pre-distort a signal prior to or during transmission in order to counteract anticipated distortion downstream in the transmission path. Accordingly, a received signal which more closely resembles an originally transmitted signal may be obtained.
In high-speed digital transmission, de-emphasis conventionally refers to having a first bit after a transition with a higher level than any other bits between such transition and a next transition. Thus, for example, the level of any and all bits between transitions may be less than the level of a first of such bits. In a transmission, bits immediately following a transition have higher frequency content than those bits that do not immediately follow a transition. Thus, bits with lower frequency content are de-emphasized, or conversely, bits with high frequency content are emphasized over bits with low frequency content. As bits with high frequency content conventionally have more losses over a channel than bits with low frequency content, such emphasis of bits with high frequency content may be used to pre-condition a signal to compensate for such losses to provide a more equalized signal when received.
Accordingly, it would be desirable and useful to provide both pre-emphasis and de-emphasis.